In high speed cutting of steel materials with high hardness, the temperature of the interface between the blade surface of a cutting tool and a work piece rises up to about 1000° C., and there is a case in which components of the work piece are burned onto the cutting tool and thus coagulation occurs. When coagulation of components of a work piece occurs, the blade surface of the cutting tool is damaged to the severe detriment of the cutting function thereof.
As a cutting tool subject to such severe thermal history, conventionally, there has been used one which is made of a hard alloy such as tungsten carbide or cermet such as titanium carbonitride as a substrate and is coated on the surface.
For example, patent document 1 proposes a surface-coated cermet cutting tool that has a hard covering layer having an excellent thermal shock resistance, which is formed on the surface of a tool base of a tungsten carbide-base hard alloy or titanium carbonitride-base cermet, and the hard covering layer is composed of the following (a) to (c):
(a) an inner layer that is composed of a Ti compound layer consisted of one layer or two or more multilayer selected from carbide layer, nitride layer, carbonitride layer, carbonate layer, and carbonitride oxide layer of Ti formed by vapor deposition, and that has an average layer thickness in the range of 3 to 20 μm;
(b) an interlayer that is composed of an aluminum oxide layer having α type crystal structure, the layer has a structure dispersed cracks generated by a heat transformation, and the aluminum oxide is produced by subjecting aluminum oxide having a κ type or θ type crystal structure to the heat transformation treatment in a state of being formed by vapor deposition in order to convert the crystal structure into an α type crystal structure, and that has an average layer thickness in the range of 3 to 15 μm; and
(c) a surface layer that is composed of an aluminum oxide layer having a κ type crystal structure in a state being formed by vapor deposition and that has an average layer thickness in the range of 0.5 to 2 μm.
Patent document 2 proposes a surface-coated cermet cutting tool that has a hard covering layer having an excellent thermal shock resistance, which is formed on the surface of a tool base of a tungsten carbide-base hard alloy or titanium carbonitride-base cermet, and the hard covering layer is composed of the following (a) and (b):
(a) an inner layer that is composed of a Ti compound layer consisted of one layer or two or more multilayer selected from carbide layer, nitride layer, carbonitride layer, carbonate layer, and carbonitride oxide layer of Ti formed by vapor deposition, and that has an average layer thickness in the range of 3 to 20 μm; and
(b) an outer multiple layer having a under side layer and a upper side layer, the under side layer is composed of an aluminum oxide layer having α type crystal structure, the under side layer has a structure dispersed cracks generated by a heat transformation, and the aluminum oxide is produced by subjecting aluminum oxide having a κ type crystal structure to the heat transformation treatment in a state of being formed by vapor deposition in order to convert the crystal structure into an α type crystal structure, and that has an average layer thickness in the range of 3 to 15 μm, and the upper side layer that is composed of an aluminum oxide layer having a α type crystal structure in a state being formed by vapor deposition and that has an average layer thickness in the range of 0.5 to 2 μm.
Patent document 3 proposes a surface-coated cermet cutting tool that has a hard covering layer having an excellent thermal shock resistance, which is formed on the surface of a tool base of a tungsten carbide-base hard alloy or titanium carbonitride-base cermet, and the hard covering layer is composed of the following (a) and (b):
(a) an inner layer that is composed of a Ti compound layer consisted of one layer or two or more multilayer selected from carbide layer, nitride layer, carbonitride layer, carbonate layer, and carbonitride oxide layer of Ti formed by vapor deposition, and that has an average layer thickness in the range of 3 to 20 μm; and
(b) an outer multiple layer having a under side layer and a upper side layer, the under side layer is composed of an aluminum oxide layer having α type crystal structure, the under side layer has a structure dispersed cracks generated by a heat treatment, and the aluminum oxide is produced by subjecting aluminum oxide having a κ type crystal structure to the heat treatment in a state of being formed by vapor deposition in order to convert the crystal structure into an α type crystal structure, and that has an average layer thickness in the range of 1 to 15 μm, and the upper side layer that is composed of an aluminum oxide layer having a α type crystal structure in a state being formed by vapor deposition and that has an average layer thickness in the range of 0.1 to 2 μm.
Patent document 4 proposes a surface-coated cermet cutting tool that has a hard covering layer having an excellent wear resistance, which is formed on the surface of a tool base of a tungsten carbide-base hard alloy or titanium carbonitride-base cermet, and the hard covering layer is composed of the following (a) and (b):
(a) an aluminum oxide layer having an average layer thickness in the range of 0.2 to 3 μm as an upper side layer;
(b) a compound nitride layer of Al and Ti having an average layer thickness in the range of 0.8 to 8 μm as a under side layer; and
the under side layer is composed of:
a maximum Al content points and a minimum Al content points exist alternatively and repeatedly at predetermined intervals along the layer thickness direction of the under side layer;
the component concentration distribution structure is such that the content ratio of Al and that of Ti continuously change from the maximum Al point to the minimum Al point and from the minimum Al point to the maximum Al point;
the minimum Al point satisfies the composition formula (Al1-XTiX)N (where X represents 0.35 to 0.60 in atomic ratio) while the maximum Al point satisfies the composition formula (Al1-YTiY)N (where Y represents 0.05 to 0.30 in atomic ratio); and
the interval between the adjacent said minimum Al point and maximum Al point is 0.01 to 0.1 μm.
Patent document 5 proposes a diamond-covered hard member whose substrate is covered by a coating of diamond and/or a diamond-like carbon, the surface average roughness of the substrate is adjusted in the range of 0.1 to 2.5 μm in Ra representation while the surface average roughness of the coating is adjusted not more than 1.5 μm in Ra representation, with Ra(c)≦Ra(s) where Ra(c) denotes the mean surface average roughness of the coating and Ra(s) denotes the mean surface average roughness of the substrate.
[Patent document 1] Publication of Japanese Patent Application 2004-188502
[Patent document 2] Publication of Japanese Patent Application 2004-188500
[Patent document 3] Publication of Japanese Patent Application 2004-188575
[Patent document 4] Publication of Japanese Patent Application 2004-351540
[Patent document 5] Publication of Japanese Patent Application Hei 10-287491